#用 pydoc 读一读关于 open，file，os，和 sys 的内容；浏览一遍即可，把有意思的东西记下来

"""open :
C:\Users\10821\lizhidexuexi>python -m pydoc open
Help on built-in function open in module io:

open(file, mode='r', buffering=-1, encoding=None, errors=None, newline=None, closefd=True, opener=None)
    Open file and return a stream.  Raise IOError upon failure.

    file is either a text or byte string giving the name (and the path
    if the file isn't in the current working directory) of the file to
    be opened or an integer file descriptor of the file to be
    wrapped. (If a file descriptor is given, it is closed when the
    returned I/O object is closed, unless closefd is set to False.)

    mode is an optional string that specifies the mode in which the file
-- More  --

file:
C:\Users\10821\lizhidexuexi>python -m pydoc file
No Python documentation found for 'file'.
Use help() to get the interactive help utility.
Use help(str) for help on the str class.

os:
C:\Users\10821\lizhidexuexi>python -m pydoc os
Help on module os:

NAME
    os - OS routines for NT or Posix depending on what system we're on.

DESCRIPTION
    This exports:
      - all functions from posix or nt, e.g. unlink, stat, etc.
      - os.path is either posixpath or ntpath
      - os.name is either 'posix' or 'nt'
      - os.curdir is a string representing the current directory (always '.')
      - os.pardir is a string representing the parent directory (always '..')
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sys:
C:\Users\10821\lizhidexuexi>python -m pydoc sys
Help on built-in module sys:

NAME
    sys

MODULE REFERENCE
    https://docs.python.org/3.6/library/sys

    The following documentation is automatically generated from the Python
    source files.  It may be incomplete, incorrect or include features that
    are considered implementation detail and may vary between Python
    implementations.  When in doubt, consult the module reference at the
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"""